The present invention relates to power semiconductor devices, and more particularly to a power device that includes a current sense feature.
It is well known to have a current sense feature to determine the current flowing through a power device, for example, a power MOSFET. In a conventional device, the current in the power device is calculated based on a predetermined ratio of the current in the current sense feature and the current in the power device.
Conventional current sense features operate well when the power device is operated in the saturation region. However, it has been observed by the inventor that when the power device is in the linear region, the current sense feature may report the status of the current inaccurately. Specifically, it has been observed that in the linear region the ratio of the current of the current sense (I(sense/linear)) to the current of the main power device is increased relative to the same ratio in the saturation region. This result indicates that the current gain in the linear region for the current sense feature of the device is limited compared to that of the power device itself.
It is believed the reduced gain in the linear region is due to the outer cells of the current sense feature exhibiting a different resistive behavior (e.g. higher resistance) in the linear region thereby causing the discrepancy between the behavior of the device during the linear region and the saturation region. Specifically, it is believed that the discrepancy in behavior may be due to the outer cells of the current sense feature having no corresponding opposing cell, doping diffusion discrepancy, and/or mis-alignment of the outer cells.